Method and system for compensation of nonlinearity or fluctuation of head-position signal

ABSTRACT

A plurality of patterns are formed so that each is deviated slightly from another in each sector in the track width direction. Then, the pattern is followed up, thereby obtaining both a full-track profile and a micro-track profile. A variation of a position signal is detected from this profile, thereby creating a table for correcting the non-linearity error of the position signal. Consequently, the distribution of the write/read-back property is measured, thereby enabling the track density to be improved. Furthermore, a variation of the position signal caused by a property variation of the head read-back element is detected and corrected, thereby enabling a high reliability and a high track density to be realized for the object magnetic recording disk apparatus.

BACKGROUND OF THE INVENTION

The present invention relates to an information recording apparatusprovided with a magnetic conversion head and a magnetic recordingmedium, more particularly to a magnetic recording disk apparatus thathas improved its track density.

Generally, in order to make a head follow up an object data track on amagnetic recording disk medium, the magnetic recording disk apparatusmust enable relative positional information between the head and themagnetic recording disk medium to be kept measured accurately and apositional deviation caused by a thermal expansion difference betweenboth magnetic recording disk medium and the arm that supports the head,as well as an influence of such a disturbance as rotation vibration ofthe spindle motor and the rotary actuator to be reduced. This is whyspecial patterns for positioning the head are recorded on the magneticrecording disk medium before the shipping. The area in which such apattern is recorded as shown in FIG. 6 is referred to as a servo area31. The servo area 31 is formed between data areas 33 via a gap area 32.After the shipping, it is inhibited that the user records data in thisservo area 31. In the servo area 31 is recorded data continuouslybetween adjacent tracks 16 in the radial direction. The servo trackwidth 311 is equal to the track pitch of the tracks 16. On the otherhand, in a data area 33, recorded data on each track 16 is separatedfrom another. The recording track width 331 is narrower than the trackpitch of the tracks 16. Actually, 60 to 100 servo areas 31 are formed atequal pitches on a round of track 16 of the magnetic recording diskmedium.

FIG. 7 shows a configuration of such a servo area 31. An ISG part 40 isa continuous pattern provided so as to reduce the influence of thedistribution of the magnetic property in the recording film and thedistribution of the flying height of the magnetic recording disk medium.The servo decoder circuit reads back the ISG part 40 by turning on theauto gain control (AGC). Upon detecting an AM part 41, the AGC is turnedoff, thereby the magnetic recording disk apparatus of the presentinvention normalizes the read-back amplitude of the subsequent burstparts 43 with the amplitude of the ISG part 40. A gray code part 42describes the track number information of each track 16 with a graycode. This part 42 often describes sector number information, as well.The burst part 43 makes a houndstooth check pattern for obtainingaccurate positional information in the radial direction. This part 43 isindispensable for following up the center of each track 16 accurately.This pattern 43 consists of a pair of A-burst 43-1 and B-burst 43-2 thatare provided as straddle the center of each track 16 alternately, aswell as C-burst 43-3 and D-burst 43-4 that are provided as straddle theedge of each track 16 alternately. A pad part 44 is a pattern providedso as to absorb the delay of the decoder circuit system to keepgenerating a clock while the servo decoder circuit reads back the servoarea 31.

The head 11 reads back the servo areas 31 while running on the positionC shown with an arrow from left to right in FIG. 7. FIG. 8(A) shows anexample of the read-back waveform at that time. To simplify thedescription, the read-back waveforms of the AM part 41, the gray codepart 42, and the pad part 44 are omitted here. The servo decoder circuit44 detects the amplitudes of the four burst parts (from the A-burst part43-1 to the D-burst part 43-4). The amplitude value of each burst partis converted to a digital value in the AD converter, then entered to aCPU. The CPU then calculates the difference between the amplitudes ofthe A-burst part 43-1 and the B-burst part 43-2, thereby finding the Nposition signal. Although an equation for normalizing the differencewith the amplitude of the ASG part 40 is described in FIG. 7, thisfunction is realized by hardware in which the servo decoder circuitlocks the AGC so as to fix the amplitude of the ISG part 40. In the sameway, the CPU obtains the Q position signal from the difference betweenthe amplitude values of the C-burst part 43-3 and the D-burst part 43-4.FIG. 8B shows the position signals of the head, which are generated asdescribed above. The N position signal becomes 0 at a position where thecenter of the head 11 straddles the A-burst part 43-1 and the B-burstpart 43-2 equally. The N position signal becomes positive or negativealmost in proportion to a deviation from this center position. Forexample, the N position signal at the position C shown in FIG. 8B can beobtained from the read-back waveform shown in FIG. 8(A) at the positionC shown in FIG. 7. Usually, it is assumed that the edges of both A-burstpart 43-1 and B-burst part 43-2 match with the center of each track 16.

The CPU inverts the status (positive/negative) of the N or Q positionsignal, whichever is smaller in absolute value, then links the signals,thereby generating a continuous position signal. This position signal isthen compared with a target position, thereby finding an optimal currentvalue to be applied to a voice coil motor 14 so as to perform suchpredetermined operations as following-up and seeking.

A technique for forming a spiral data track itself is disclosed inJapanese Published Unexamined Patent Application No. 62-204476, No.63-112874, and No. 61-296531 respectively. A technique for formingspiral servo information itself is disclosed in FIG. 1 of JapanesePublished Unexamined Patent Application No. 62-204476.

BRIEF SUMMARY OF THE INVENTION

The above conventional techniques, however, have been confronted with aproblem that non-uniformity of the direction of magnetization in theread-back element degrades the linear accuracy of the position signal,thereby the radial position of the head cannot be controlled accurately.In addition, those conventional techniques have also been confrontedwith a problem that because the detection accuracy of the positionsignal is degraded by a property variation of the read-back element, theradial position of the head cannot be controlled accurately.

In the recent years, however, it is common that a high read sensitivityhead is used to increase the recording density of the object magneticrecording disk apparatus. For example, there are well-known techniquesfor using a read-back head that employs a magnetoresistive element (MRelement) that makes good use of the magnetoresistive effect of themagnetic film itself, a giant magnetoresistive element (GMR element)that has improved the magnetoresistive effect with a non-magnetic filmsandwiched by magnetic films, or a tunnel magnetoresistive element (TMRelement) that has improved the magnetoresistive effect more with use ofa phenomenon that a tunnel current is changed by an external magneticfield significantly. Those techniques are all effective, since each ofthose magnetoresistive elements can obtain a favorable SN ratio even inreading back fine recorded patterns on magnetic recording disks, therebythe bit density of the object magnetic recording disk apparatus can beimproved.

Generally, both ends of a magnetoresistive element are structured so asto enable a bias magnetic field (vertical bias magnetic field) to beapplied in the width direction of the track, thereby forming themagnetic film of the element in a single magnetic domain structure.Consequently, the read-back sensitivity is degraded with respect to thestrength of the leakage magnetic field of the object disk at both endsof the element, thereby the output is not made in uniform in the widthdirection of the track. In addition, because the magnetizing directionis disturbed at both ends of the element, the amplitude value may differsignificantly between positive side and negative side of the read-backwaveform. And furthermore, the non-uniformity of the magnetizingdirection, which is a problem mentioned here, may be varied in variousforms due to the recording magnetic field generated by the write elementprovided adjacently to the magnetoresistive element. This phenomenon isreferred to as a property variation of the read-back element. Thisproperty variation of the read-back element may also occur due to achange of the flying attitude of the head caused by a wear, a flaw, anda contaminant thereon.

Because the read-back sensitivity is low at both ends of the element,the read-back amplitude of the burst part 43 is not proportional to theradial position of the head. Both of N and Q position signals also donot become proportional to the radial position of the head exactly. Ifany asymmetrical component of the vertical amplitude is contained in theread-back waveform of the burst part 43, then the constant of thedecoder circuit comes to depend on the position signal significantly,thereby the errors of both N and Q position signals become more serious.Because of those negative factors, the N and Q position signals of themagnetic recording disk apparatus that uses a magnetoresistive elementdo not become linear as shown in FIG. 8B. There is a technique forimproving the accuracy for detecting the error level referred to as anon-linearity error of this position signal by creating a correctiontable and using the table. In this case, however, a correction tablemust be prepared for each head mounted in the magnetic recording diskapparatus and the table must be recorded in the memory of the packageboard 17 or in part of the management area on the disk 12 beforeshipping. Consequently, the management of production processes becomescomplicated, and furthermore, the difference among properties of decodercircuits cannot be corrected even with this technique. Those factorshave thus been an obstacle for the improvement of the track density ofthe apparatus.

Furthermore, the center of a track to follow up may be offset due to achange of the non-linearity error level if a property variation occursin the read-back element. To avoid such a read-back error to occur dueto a change of the property variation of the read-back element,therefore, a current is applied to the write element so as to execute adummy write operation that applies an external magnetic field to theread-back element intentionally, thereby eliminating the propertyvariation. This is a well-known technique. And yet, there is stillanother problem that must be solved. The problem is a fact that thecontent of the variation in a magnetized state differs between propertyvariation of the read-back element related to the non-linearity of theposition signal and the property variation of the read-back elementrelated to a read-back error. The technique that performs a dummy writeoperation after a read-back error occurs cannot avoid a possibility thatan offset from a target track, thereby overwriting is done on anadjacent track. This has been a factor for degrading the reliability ofthe magnetic recording disk apparatus.

This is why there has been expected appearance of a new technique thatenables the non-linearity error of the position signal caused by theread-back property of the head and the servo decoder circuit property tobe corrected so as to improve the positioning accuracy, therebydetecting the property variation of the read-back element related to thenon-linearity error of the position signal and improve the data trackdensity of the magnetic recording disk apparatus that employs amagnetoresistive element as the read-back element. It is thus possibleto prevent the fatal error that overwrites data on adjacent tracks so asto improve the reliability of the apparatus.

In order to achieve the above objects, the magnetic recording diskapparatus of the present invention comprises a magnetic recording diskmedium provided with a plurality of tracks formed thereon in aconcentric circle pattern and a servo area formed on a part of eachtracks and used to record a servo pattern; a magnetic recording headprovided with a read-back element and a write element; and a servodecoder circuit for generating a head position signal from the servopattern formed on the magnetic recording disk medium; wherein aplurality of patterns are disposed in an area different from the servoarea on the disk medium. Each of a plurality of the patterns is deviatedfrom another in the radial direction of the track at least by a widthnarrower than the width of the read-back element of the head.

Furthermore, a plurality of full tracks are disposed in some radialareas on the disk so that each of the full tracks is deviated slightlyfrom another in the radial direction of the disk and the amplitude ofthe read-back waveform of each of those full tracks is detected whilefollowing up the track, thereby measuring the profile of each full trackfrom the amplitude of the read-back waveform.

Furthermore, in the magnetic recording disk apparatus of the presentinvention, a plurality of micro-tracks are disposed in some radial areason the disk so that each of those micro-tracks is deviated slightly fromanother in the radial direction of the disk and the amplitude of theread-back waveform of each of a plurality of the micro-tracks isdetected while the track is followed up, thereby measuring the profileof the micro-track from the amplitude of the read-back waveform.

The magnetic recording disk apparatus is provided with a function forcalculating an effective write or read-back width of the head from theprofile of the full-track or the micro-track. The magnetic recordingdisk apparatus is also provided with a function for correcting thenon-linearity of the head position signal from the profile of thefull-track or the micro-track. The magnetic recording disk apparatus isfurther provided with a function for detecting a variation of the headposition signal from the profile of the full-track or the micro-track.The magnetic recording disk apparatus is further provided with afunction for detecting a variation of the head read-back property fromthe profile of the micro-track. In addition, the magnetic recording diskapparatus is further provided with a function for correcting thevariation if the variation is out of a preset range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the first example of a pattern for detection full-trackprofile of the present invention.

FIG. 2 shows the second example of a pattern for detection full-trackprofile of the present invention.

FIG. 3 is a top view of a structure of a magnetic recording disk.

FIG. 4 is a cross sectional view of the structure of the magneticrecording disk.

FIG. 5 is a bottom view of part of the magnetic recording disk.

FIG. 6 is an explanatory view of a structure of a sector of the magneticrecording disk apparatus.

FIG. 7 is an explanatory view of a structure of a servo area of themagnetic recording disk apparatus.

FIG. 8 shows a process for calculating a position signal from a servoread-back waveform.

FIG. 9 shows a process for creating a pattern for detection full-trackprofile of the present invention.

FIG. 10 is a block diagram of a pattern detector circuit of the presentinvention.

FIG. 11 shows an example of a full-track profile detected from a patternof the present invention.

FIG. 12 shows the third example of the pattern for detection full-trackprofile of the present invention.

FIG. 13 shows the fourth example of the pattern for detection full-trackprofile of the present invention.

FIG. 14 shows the first example of a pattern for detection micro-trackprofile of the present invention.

FIG. 15 shows the second example of the pattern for detectionmicro-track profile of the present invention.

FIG. 16 shows an example of the micro-track profile detected from apattern of the present invention.

FIG. 17 shows how to calculate an effective read-back width and aneffective write width of a head.

FIG. 18 shows an example of how to correct a head position signal.

FIG. 19 shows an example of how to detect and correct a variation of thehead position signal from a full-track profile.

FIG. 20 shows an example of how to detect and correct a propertyvariation of a read-back element from a profile of a micro-track.

DESCRIPTION OF THE SYMBOLS

11 . . . Head 12 . . . Disk 13 . . . Rotary Actuator 14 . . . Voice CoilMotor 15 . . . Head Amplifier 16 . . . Track 17 . . . Package Board 31 .. . Servo Area 32 . . . Gap Part 33 . . . Data Area 40 . . . ISG Part 41. . . AM Part 42 . . . Gray Code Part 43 . . . Burst Part 44 . . . PadPart 51 . . . Pattern for Detection Full-track Profile 52 . . . Patternfor Detection Full-track Profile 53 . . . Pattern for DetectionFull-track Profile 54 . . . Pattern for Detection Full-track Profile 55. . . Micro Servo Area 56 . . . Pattern for Detection Micro-trackProfile 57 . . . Pattern for Detection Micro-track Profile

DETAILED DESCRIPTION OF THE INVENTION EMBODIMENT 1

FIG. 3 shows a top inside view of an enclosure of a magnetic recordingdisk apparatus and FIG. 4 shows a cross sectional view of the apparatus.The main parts composing the magnetic recording disk apparatus are asshown in FIGS. 3 and 4, that is, six heads 11; three disks 12; a rotaryactuator 13; a voice coil motor 14; a head amplifier 15; a package board17, etc. The three disks 12 are fixed to a hub and each of the disks 12is rotated around the point A by a spindle motor. The six heads 11 arefixed to a comb-like arm and each of the heads 11 is rotated around thepoint B by the rotary actuator 13. With this mechanism composed asdescribed above, each head 11 can move freely in the radial direction ofthe disk 12. In the package board 17 are mounted a central processingunit (CPU) used for controlling; a hard disk controller (HDC); aninterface circuit; a memory; a signal processing unit, etc. Because theS/N ratio and the transfer rate are improved more if the head amplifier15 is disposed near to each head 11, the head amplifier 15 is notmounted on the package board 17; it is often mounted in the enclosure.

FIG. 5 shows a top partial view of the disk 12. Each head 11 is fixed ata radial position of any of data tracks 16-1, 16-2, . . . on a disk 12by the rotary actuator 13 and used to write and read back information inand from the data tracks 16 electrically. Data tracks 16 are formed atequal pitches in a concentric circle pattern.

Although only four data tracks 16-1 to 16-4 are shown in the explanatoryview in FIG. 5, there are more than 8000 data tracks actually formed atpitches of 2 μm or under on the disk 12.

FIG. 1 shows a configuration of a pattern for detection full-trackprofile 51, which is used to detect the profile of each full-track(provided with a width equal to the width of a recording track in a dataarea) in an embodiment of the present invention.

In FIG. 1, the horizontal direction indicates the circumferentialdirection of the disk 12 and the vertical direction indicates the radialdirection of the disk 12. Each head 11 moves both in the direction inwhich the head runs and in the direction shown with an arrow at a speedof 6 to 11 m/sec relatively to the disk 12. In FIG. 1 an area assignedwith a sector number 1 is duplicated at both right and left sides. Thisis just appearance, because a one round pattern on the disk 12 formed incircumference is drawn linearly. The areas on both right and left sidesare thus in one and the same sector 1 actually. The areas assigned witha sector number 72 are also in one and the same area actually. Someservo areas 31 shown in FIG. 1 are composed just like those described inthe related art. The magnetic recording disk apparatus composed asdescribed above are provided with 72 servo areas 31 formed at equalpitches on a round of the disk 12. A total of the 72 servo areas 31occupies a length of about 7% of a round of the disk 12. The track pitch(Tp) is 1.78 μm and the symbol 2×Tp shown in FIG. 1 means an equivalenceto 3.55 um.

A pattern for detection full-track profile 51 is recorded between servoareas 31. The pattern for detection full-track profile 51 is a patternhaving a width equal to that of the recording track 331 in each dataarea 33. In this configuration of the disk 12, the pattern for detectionfull-track profile 51 is recorded as simple repetitive patterns to beinverted at a 20 MHz clock. If this pattern 51 is read back from atrack, the pattern 51 takes a waveform close to a 10 MHz sine wave.Unlike the pattern in a normal data area 33, it is characterized by theuse of a simple magnetizing pattern. None of such magnetizing patternsas the PLL sink area, the data address mark, the ECC, the CRC is notused.

The patterns for detection full-track profile 51 recorded in the areawhose sector numbers are 1 and 2 respectively are magnetized patternshaving the same frequency, but they are deviated from each other only by0.05 μm in the radial direction of the disk. In addition, the patternsfor detection full-track profile 51 recorded in the areas whose sectornumbers are 3 to 72 are deviated from each other only by 0.05 μmsequentially in the same direction. Consequently, the patterns fordetection full-track profile 51 recorded in the areas whose sectornumbers are 1 and 72 are deviated from each other only by 3.55 μmsequentially in the radial direction of the disk. The 3.55 μm is doublethe track pitch.

Hereunder, a description will be made for a process for writing thepattern shown in FIG. 1 described above with reference to FIG. 9. In theservo area writing process included in the manufacturing processescarried out in a factory, the pattern is written with use of amanufacturing apparatus referred to as a servo track writer. The servotrack writer uses an external laser measuring apparatus to drive therotary actuator 13 while measuring the position of each head 11accurately. At first, data is written in servo areas 31 entirely in thefull radius range of the disk 12. After that, control goes to theprocess for writing a pattern for detection full-track profile 51.

FIG. 9(A) shows a head 11 moved only by 0.05 μm in the radial directionupto a position where a pattern for detection full-track profile 51 isrecorded in an area whose sector number is 1, then another pattern fordetection full-track profile 51 is recorded in an area whose sectornumber is 2. This state of the disk 12 indicates that the disk 12 hasbeen rotated once. FIG. 9B shows the state of the disk 12 after it isrotated twice. This state indicates that the head 11 is moved only by0.05 μm in the radial direction upto the next writing position after apattern for detection full-track profile 51 is written in the area whosesector number is 2. FIG. 9C shows a state of the disk 12 started atsector number 3 has just finished the pattern writing after 72 times ofrotation. Finally, the patterns for detection full-track profile 51written in the areas whose sector numbers are 1 and 72 are deviated fromeach other by 3.55 μm sequentially in the radial direction of the disk12. The time required for forming the 72 patterns described above, ifthe disk 12 is rotated at 400 rpm, is 72×0.015=1.08 s. In this case, itis premised that the disk 12 is rotated once at 0.015 s. On thecontrary, the time for forming a normal servo area 31 is

8000×2×0.015+8000×2×0.015×⅓=320 s

if the disk 12 is rotated at 4000 rpm and servo writing is done on 8000tracks at ½ pitches and the disk is rotated by ⅓ while the head is movedto an adjacent track. The time required for adding a pattern fordetection full-track profile 51 of the present invention is very slightwhen compared with the time required for a normal servo track writingprocess.

FIG. 2 shows a configuration of the pattern for detection full-trackprofile 52 as another embodiment of the present invention. The verticaldirection in FIG. 2 is the radial direction of the disk 12 and thepattern 52 consists of 72 servo areas just like in the configuration ofthe pattern 51 shown in FIG. 1. In FIG. 2, however, the track pitch (Tp)is 1.75 μm and the symbol 2×Tp shown in FIG. 2 means an equivalence to3.5 um.

The patterns for detection full-track profile 52 written in the areaswhose sector numbers are 1 and 2 are magnetized patterns having the samefrequency, but they are deviated from each other by 0.1 μm in the radialdirection of the disk. In addition, the patterns for detectionfull-track profile 52 written in the areas whose sector numbers are 3 to35 are deviated from each another by 0.1 μm sequentially in the radialdirection of the disk. The patterns for. detection full-track profile 52written in the areas whose sector numbers are 1 and 35 are deviated fromeach other only by 3.5 μm sequentially in the radial direction of thedisk. The 3.5 μm is an equivalence to double the track pitch. In thearea whose sector number is 36 is written a pattern for detectionfull-track profile 52. The area is written in the same radial positionas that of the area whose sector number is 1. In the same way, in theareas whose sector numbers are 37 to 72 are written patterns fordetection full-track profile 52 in the same radial positions as those ofthe areas whose sector numbers are 2 to 35.

The pattern 52 shown in FIG. 2, when compared with the pattern 51 shownin FIG. 1, is deviated from another only by a half, so the profiledetecting accuracy also becomes a half. On the contrary, because thesame pattern is repeated twice while the disk is rotated once, the errorto be caused by the mechanical vibration when in writing and in readingback patterns can be reduced with employment of an averaging processing.It depends on the mechanical vibration content of the servo track writerand the spindle motor which pattern can detect the full-track profilemore accurately. Although the pattern described here is formed bydividing a 2×Tp track width by 36 within a range of ½-round of the disk,the track width, the disk rotation distance, and the dividing number canbe decided freely.

FIG. 10 shows a block diagram of a decoder circuit for detectingfull-track profiles from the pattern of the present invention.

In order to simplify the configuration, the decoder circuit system ofthe present invention is just composed by adding a band-pass filter(BPF), an amplifier (AMP), and a switch to the conventional servodecoder circuit. Read-back data output from a head 11 is amplified by100 to 200 times in the amplifier 15, then high frequency componentnoises are removed from the data with use of a low-pass filter (LPF).The auto gain controller (AGC), as described in the related art withreference to FIGS. 7 and 8, adjusts the amplitude of read-back waveformsso as to fix the amplitude of the ISG part 40. When the address markdetector (AM detector) detects the AM part 41 from a signal obtained byconverting a read-back waveform to a digital waveform in the peakdetector, the AGC is turned off to fix the amplified gain, thereby thedetecting accuracy of the pattern for detection full-track profile isprevented from non-uniformity of magnetic property of the disk andinfluence of the disk flying height.

The center frequency of the BPF is set to 10 MHz, which is the same asthe read-back frequency of the pattern for detection full-track profile,so that noise is removed from the signal component of the pattern,thereby the detecting accuracy is improved. The switch selects the BPFside when in detecting a full-track profile. When in detecting amicro-track profile to be described later, the switch selects theamplifier (AMP) side. The bit length of the pattern for detectionfull-track profile can be set longer than the burst part 43 in a normalservo area 31, so the integral time constant of the integrator is setlong according to the length of the pattern so as to improve thedetecting accuracy. The A/D converter converts the amplitude of thepattern detected by the integrator to a digital value. The centralprocessing unit (CPU) and the hard disk controller (HDC) are used tocontrol the timings of the AGC, the switch, the integrator, and the A/Dconverter.

FIG. 11(A) shows a case in which the pattern shown in FIG. 2 is writtenby a head 11 on a disk 12 built in a magnetic recording disk apparatusand a read-back amplitude is detected in each sector. In FIG. 11(A), thehorizontal axis indicates sector numbers. Sector numbers 1 to 72 areequivalent to sectors on a round of the disk. The vertical axisindicates output values from the A/D converter that detects theamplitude of each sector. The read-back profiles 1 and 2 indicated withwhite and black circles are not the same, since they are influenced bythe mechanical vibration of the servo track writer when in writingpatterns and by the mechanical vibration of the spindle motor when inreading back patterns. FIG. 11B shows an average of the profiles 1 and 2shown in FIG. 11(A). In FIG. 11B, the horizontal axis indicates theaverage profile converted in units of um. When the radial position ofthe head exceeds the ±1.2 μm range, the output,value becomes a value onthe noise level of the detection system. This profile is a full-trackprofile detected automatically on the disk built in the magneticrecording disk apparatus. The horizontal axis is calibrated with theaccuracy of the laser measuring apparatus of the servo track writer.

FIG. 12 shows a configuration of a pattern for detection full-trackprofile 53 as further another embodiment of the present invention. Inorder to improve the detecting accuracy, the pattern for detectionfull-track profile 53 is multiplexed before it is written, so that thepattern 53 enables an averaging processing to be performed as many aspossible. In FIG. 12, the vertical direction is the radial direction ofthe disk 12 and the horizontal direction is the circumferentialdirection of the disk 12. Although there is only one servo area whosesector number is 1 in an expanded view in FIG. 12, there are actually 72servo areas 31. The track pitch is 1.78 μm and the symbol 2×Tp shown inFIG. 12 means an equivalence to 3.55 just like in the configuration ofthe pattern shown in FIG. 1.

In order to multiplex each pattern for detection full-track profile 53before it is written, the pattern length is set shorter than that shownin FIG. 1. This pattern is written by 72 times in an area whose sectornumber is 1 so that each pattern is deviated from another by 0.05 μmsequentially in the radial direction of the disk. Consequently, thepatterns at both start and end of each sector are deviated from eachother by 3.55 μm in the radial direction of the disk. The 3.55 μm is alength equivalent to double the track pitch. In addition, the sameconfiguration pattern as that written in the area whose sector number is1 is thus written in the areas whose sector numbers are 2 to 72.

The pattern 53 shown in FIG. 12, when compared with the pattern 51 shownin FIG. 1, can reduce the error occurrence caused by the mechanicalvibration when in writing and reading back patterns significantly withexecution of an averaging processing, since the same pattern is repeatedby 72 times while the disk 12 is rotated once. On the other hand,because each pattern for detection full-track profile 53 is short, thisconfiguration arises problems that the pattern amplitude detectingaccuracy is degraded and a high accuracy is required for generating aclock from the detector. Although the pattern in this embodiment isformed by dividing a 2×Tp track width by 72 within a sector range, thetrack width and the dividing number may be decided freely.

FIG. 13 shows a configuration of a pattern for detection full-trackprofile 54 as further another embodiment of the present invention. Inorder to solve the problems of the configuration shown in FIG. 12 andimprove the detecting accuracy more, the pattern is multiplexed less innumber and the number of servo areas is increased in the configurationshown in this FIG. 13. In FIG. 13, the vertical direction is the radialdirection of the disk 12 and the horizontal direction is thecircumferential direction of the disk 12. Although only the servo areaswhose sector numbers are 1 to 18 are shown in the expanded view in FIG.13, there are actually 72 servo areas 31. The track pitch is 1.78 μm andthe symbol 2×Tp shown in FIG. 13 means an equivalence to 3.55 just likein the configuration shown in FIG. 1.

Three micro-servo areas 55 are provided at equal pitches between servoareas respectively. The configuration of each micro-servo area 55 is thesame as that described in the related art with reference to FIG. 7except that the gray code part 42 is removed. A micro-servo area 55 isprovided only in a track width measuring zone. In a data zone where adata area 33 exists is provided only a normal servo area 31. The patternfor detection full-track profile 54 is provided in an area between aservo area 31 and a micro-servo area 55 or between micro-servo areas 55.In the sector number=1 area, four patterns for detection full-trackprofile can be disposed so that each pattern is deviated from another by0.05 μm sequentially in the radial direction of the disk. The fourthpattern for detection full-track profile in the sector number=1 area isdeviated by 0.05 μm from the first pattern for detection full-trackprofile in the sector number=2 area. In the same way, 72 patterns fordetection full-track profile 54 can be written in the areas whose sectornumbers are 1 to 18 sequentially. The first pattern for detectionfull-track profile in the sector number=1 area is deviated by 3.55 μmfrom the fourth pattern 54 in the sector number=18 area in the radialdirection of the disk. The 3.55 μm is an equivalence to double the trackpitch. In addition, the same configuration pattern as that written inthe areas whose sector numbers are 1 to 18 is written in the areas whosesector numbers are 37 to 54 and 55 to 72.

The pattern 54 shown in FIG. 13 is repeated four times while the disk.12 is rotated once. These four patterns are averaged, thereby the errorcaused by the mechanical vibration when in writing and reading backpatterns can be reduced more than the embodiments shown in FIGS. 1 and 2in which patterns 51 and 52 are used. In addition, because each patternis extended and a micro-servo area 55 is provided, it is possible tosolve the problems related to the pattern amplitude detecting accuracyand the clock generation accuracy of the detector circuit more than whenthe pattern shown in FIG. 12 is used. Although a pattern is formed bydividing a 2×Tp track width by 72 within a range of ¼ rotation of thedisk in this embodiment, the track width, the disk rotation distance,and the dividing number may be decided freely.

According to the above embodiment, patterns for detection full-trackprofile on a disk built in the object magnetic recording disk apparatuscan be detected automatically very accurately by reducing the erroroccurrence caused by the mechanical vibration when in writing andreading back patterns with employment of the pattern configuration, thewriting process, and the detector circuit system as described in thisembodiment.

EMBODIMENT 2

FIG. 14 shows a configuration of a pattern for detection micro-trackprofile 56, which is a pattern for detecting a micro-track (having awidth narrower than that of the recording track in each data area)profile as an embodiment of the present invention. This patternconfiguration has many common items as the pattern for detectionfull-track profile 52 shown in FIG. 2. The pattern for detectionmicro-track profile 56 is a pattern having a width narrower than that ofthe recording track 331 in each data area 33. Just like the patternconfiguration shown in FIG. 2, this pattern configuration includes 72servo areas 31, the track pitch is 1.75 um, and the symbol 2×Tp means anequivalence to 3.5 um.

A pattern for detection micro-track profile 56 is written between servoareas 31 respectively. The pattern for detection micro-track profile 56is formed with 20 MHz patterns repeated simply and having a narrow trackwidth of not more than ¼ of the track width of the write element.Although the patterns for detection micro-track profile 56 written inthe areas whose sector numbers are 1 and 2 are magnetized patternshaving the same frequency, they are deviated from each other by 0.05 μmin the radial direction of the disk. In addition, the patterns fordetection micro-track profile 56 written in the areas whose sectornumbers are 3 to 72 are deviated by 0.05 μm from each anothersequentially in the radial direction of the disk. Consequently, thepatterns for detection micro-track profile 56 written in the areas whosesector numbers are 1 and 72 are deviated from each other by 3.55 μm inthe radial direction of the disk. The 3.55 μm means an equivalence todouble the track pitch.

To write the patterns for detection micro-track profile 56, amanufacturing apparatus referred to as a servo track writer is used inthe manufacturing processes in the object factory. This is to form thepattern 56 having a track width narrower than that of the write elementof the head very accurately. In order to form a pattern for detectionmicro-track profile 56, the disk must be rotated twice. At the firstrotation, a full track is written in the sector number=1 area with 20MHz patterns repeated simply, then the head is deviated by 0.3 μm inwardin the radial direction of the disk. In this state, it is awaited untilthe disk is rotated up to the sector number=1 area, then a DC current isapplied to the head in the sector number=2 area on the second rotationso as to erase the patterns written in the first rotation from one sideand form a pattern whose track width is narrower than that of the writeelement of the head. The width of the pattern for detection micro-trackprofile 56 formed actually is narrower than 0.3 μm deviated when inerasing. This is caused by a phenomenon that the width for the head toerase old data is wider than the width for the head to write new data.

Although the pattern described in this embodiment is formed by dividingthe 2×Tp track width by 36 within a range of ½ rotation of the disk, thetrack width, the disk rotation distance, and the dividing number may bedecided freely.

It is possible to reduce the time for forming 72 patterns formicro-track profile by carrying out both write process at the firstrotation and erase process at the second rotation as described above atthe same head position. It does not need any time for rotating the diskby the number of times double the 72 patterns. For example, because thehead position where a pattern is erased from one side in the sectornumber=1 area is the same as the head position where a pattern iswritten in the sector number=7 area, these two write and erase processescan be carried out while the disk is rotated once. The use of thismethod will thus be able to reduce the time for forming 72 patterns fordetection micro-track profile upto a time for rotating the disk by6+72+6=84 times.

The configuration of the decoder circuit for detecting micro-trackprofiles from the pattern of the present invention is almost the same asthat described above in the embodiment 1 with reference to FIG. 10.However, when compared with the read-back amplitude of a full-track, theread-back amplitude of a micro-track is as small as about ⅓ to {fraction(1/10)}, so 3 to 10 times of amplifiers (AMP) are disposed serially andthe switch is set to AMP. Functions of other components are the same asthose in the embodiment 1.

FIG. 16(A) shows an example of detection of the read-back amplitude of apattern for detection micro-track profile 56 shown in FIG. 14 in eachsector. The pattern for detection micro-track profile is written by ahead 11 on a disk 12 built in the object magnetic recording diskapparatus. The horizontal axis indicates sector numbers. Sector numbers1 to 72 are equivalent to the number of sectors on one round of thedisk. The vertical axis indicates output values from the A/D converterthat detects the amplitude of each sector. The profile 1 indicated withwhite circles and the profile 2 indicated with black circles may notbecome identical sometimes due to the influence of the mechanicalvibration of the servo track writer when in writing of the pattern 56 orthe mechanical vibration of the spindle motor when in reading back thepattern 56.

FIG. 16B shows an average of the read-back profiles 1 and 2 shown inFIG. 16 (A). The value in the horizontal axis is converted to a value inunits of um. The output value, when the radial position of the head iswithin a range of ±1.1 um, is a value on the noise level of thedetection system. This profile is a micro-track profile detectedautomatically on the disk built in the magnetic recording diskapparatus. The horizontal axis is calibrated with the accuracy of thelaser measuring apparatus of the servo track writer.

FIG. 15 shows a configuration of a pattern for detection micro-trackprofile 57 as another embodiment of the present invention. In FIG. 15,the vertical direction is the radial direction of the disk 12 and thehorizontal direction is the circumferential direction of the disk 12.The pattern for detection micro-track profile 57 has many common pointsto those of the pattern for detection micro-track profile 54 shown inFIG. 13. Just like in the configuration of the pattern 54 shown in FIG.13, there are a total of 216 micro-servo areas 55 only in the trackwidth measuring zone, the track pitch is 1.78 um, and the symbol 2×Tpmeans an equivalence to 3.55 um. In FIG. 15, of the 72 servo areas 31,only the areas whose sector numbers 1 to 18 are shown in an expandedview.

A pattern for detection micro-track profile 57 is written between aservo area 31 and a micro-servo area 55 respectively. In order toimprove the detection accuracy more, the pattern 57 is multiplexed sothat the number of servo areas is increased.

Four patterns for detection micro-track profile can be disposed in thesector number=1 area so that each of them is written so as to bedeviated from another by 0.05 μm sequentially in the radial direction ofthe disk. The fourth pattern for detection micro-track profile in thesector number=1 area is also deviated by 0.05 μm from the first patternfor detection micro-track profile in the sector number=2 area. In thesame way, 72 patterns for detection micro-track profile can be writtensequentially in the areas whose sector numbers are 1 to 18. The firstpattern in the sector number=1 area is deviated by 3.55 μm from thefourth pattern in the sector number=18 area in the radial direction ofthe disk. The 3.55 μm is double the track pitch. In addition, the sameconfiguration pattern as that written in the areas whose sector numbersare 1 to 18 is written in the areas whose sector numbers are 19 to 36,37 to 54, and 55 to 72 respectively.

The pattern 57 shown in FIG. 15 is repeated four times while the disk 12is rotated once. Those four patterns 54 are averaged, thereby the erroroccurrence caused by the mechanical vibration when in writing or readingback patterns can be reduced more than when the pattern shown in FIG. 14is used. In addition, because the pattern 57 is provided withmicro-servo areas 55, the pattern amplitude detection accuracy can beimproved more than when the pattern 56 shown in FIG. 14 is used.Although a pattern is formed by dividing the 2×Tp track width by 72within a range of ¼-round of the disk in this embodiment, the trackwidth, the disk rotation distance, and the dividing number may bedecided freely.

With the employment of the pattern configuration, the writing process,and the detector circuit system described in this embodiment, thepresent invention has made it possible to reduce the error occurrencecaused by the mechanical vibration when in writing and reading backpatterns, thereby enabling micro-track profiles on a disk built in theobject magnetic recording disk apparatus to be detected very accurately.

Next, a description will be made for a method for calculating aneffective read-back width and an effective write width from bothmicro-track profile and full-track profile described above withreference to FIG. 17.

The read-back profile from a micro-track having a width narrower thanthat of the write element track of the head matches with the sensitivitydistribution profile of the head in the leakage magnetic field of thedisk in the track width direction. Consequently, the read-back profilesfrom the satisfactorily narrow micro-track are integrated, thereby eachprofile from the recording tracks in various areas can be calculated.

FIG. 17(A) shows a normalized result of convolution integral of themicro-track profile shown in FIG. 16B and a step function with themaximum value. Because values not within a range of ±1.1 μm of themicro-track profile is noise level ones, they are removed by a simplesubtraction respectively. The horizontal axis in the graph correspondsto the radial position at the rising of the step function from 0 to 1.This profile matches with the read-back profile at one side from a varywide recording track. If the effective read-back width of the read-backhead is assumed to be a width that can output 5 to 95% of the read-backprofile at one side from the very wide recording track, the effectiveread-back width will be found to be 1.1 μm as shown in FIG. 17(A).

Each white circle shown in FIG. 17B is a full-track profile shown inFIG. 11B. The solid line indicates a result of normalization of theconvolution integral of the micro-track profile shown in FIG. 16B and arectangular function with the maximum value. Because values not within arange of ±1.1 μm of the micro-track profile are noise level ones, theyare removed by a simple subtraction respectively. In FIG. 17B, thehorizontal axis is shifted so as to match each calculation result withthe right side profile each time the rectangular function width ischanged to 1.3, 1.4, and 1.5 μm sequentially. Because the result ofintegrating by 1.4 μm matches with the measured full-track profile mostsatisfactorily, the effective write width will become 1.4 um. Actually,it can be judged with the value of the root sum of the differencebetween both values whether or not the measured value matches with thecalculated value.

Next, a description will be made for a method for finding a sensitivitycorrection coefficient of a head position signal from a micro-track or afull-track profile with reference to FIG. 18.

FIG. 18(A) shows that a curve (measured value(=A-burst)) is forfull-track profiles detected just like in the embodiment 1. This curvecan also be found by convolution integral of micro-track profilesperformed with use of a rectangular function, which is detected justlike in the embodiment 2. The (B-burst) curve is obtained by shifting ameasured value to the right (inner circumferential direction) accordingto a value that is the track pitch. These two curves are equivalent tothe A amplitude of A-burst 43-1 and the B amplitude of B-burst 43-2described in the related art with reference to FIGS. 7 and 8. Becausethe AGC is controlled so as to fix the amplitude of the ISG part 40,both A and B amplitudes are normalized with the ISG amplitude. Themeasured value curve shown in FIG. 18B indicates values obtained bysubtracting the B amplitude from this A amplitude respectively and it isequivalent to the N position signal shown in FIG. 18B. As described inthe PROBLEMS TO BE SOLVED BY THE INVENTION, this measured N positionsignal curve does not become a straight line in many cases.

In the case of the conventional magnetic recording disk apparatus,because the apparatus is controlled on the assumption that the valueshown on the vertical axis in FIG. 18B is related to a true positionproportionally, an error comes to occur in a radial position of thehead. This error becomes a problem especially in an operation referredto as a micro-jog that corrects an offset between the read-back elementand the write element. The offset between the read-back element and thewrite element is changed according to the yaw angle of the slider, sothe N position signal must match with an ideal straight line shown inFIG. 18B at a given radial position of the head. In addition, the changeof the position signal with respect to the radial position of the headis lowered at a position near to the linkage between N and Q positionsignals, so the servo loop gain is further lowered as the value of ±0.6μm comes closer in FIG. 12B. The positioning accuracy is thus degraded.These errors are referred to as non-linearity errors of positionsignals.

FIG. 18C shows a value obtained by dividing an ideal line by a measuredline. The value can be used as a sensitivity correction coefficient ofposition signals. This coefficient is multiplied by a position signaldetected by the servo decoder circuit, thereby enabling thenon-linearity error occurrence of the above position signal to bereduced significantly. The sensitivity correction coefficient of theposition signal found here is written beforehand in the memory of thepackage board 17 or in part of the management area of the disk 12 foreach head.

The burst part 43 of the servo area 31 is usually formed with aplurality of write operations in the width direction of the track, sothe width is often different from the width of the normal data track.Consequently, when finding a sensitivity correction coefficient of theposition signal of the head, the width of the pattern for detectionfull-track profile must be adjusted to the width of the track in theburst part 43. In addition, when finding a sensitivity correctioncoefficient of the position signal of the head through convolutionintegral of a micro-track read-back profile and a rectangular function,the width of the rectangular function must be adjusted to the trackwidth of the actual burst part 43. To find a sensitivity correctioncoefficient of the position signal of the head more accurately, aplurality of patterns for detection full-track profile must be preparedat different radial positions of the head and a sensitivity correctioncoefficient of the position signal in each of those radial positions canbe calculated.

According to this embodiment, because a correction table is created foreach of the heads mounted in the object magnetic recording diskapparatus, it is possible to improve the positioning accuracy of thehead, thereby enabling the track density of the apparatus to be improvedmore. The creation process of the correction tables can be automated forthe apparatus independently, so that the process can be included in theproduction processes easily. In addition, those correction tables arecreated with use of the servo decoder circuit provided in eachapparatus, so the property variation of the servo decoder circuit canalso be corrected at the same time.

Next, a description will be made for a method for detecting a variationof the head position signal with use of a pattern for detectionfull-track profile with reference to FIG. 19.

In steps 1 to 3 shown in FIG. 19(A), the head is instructed to seek atrack width measuring zone so as to follow the track, thereby detectinga full-track profile from a pattern for detection micro-track profile.Those processes are the same as those described in the embodiment 1. Instep 4, a root sum (RMS value) is calculated from the difference betweenthe detected full-track profile and the reference profile. Thisreference profile is a measured value obtained from each head andwritten in the memory of the package board 17 or in part of themanagement area of the disk 12 beforehand. In step 5, the RMS value iscompared with the upper limit value. If the RMS value is less than theupper limit value, the state is judged to be normal, thus the processingis finished.

FIG. 19B shows a full-track profile measured at a normal time and areference profile. After 20 times of measurement, the average of the RMSvalues was 8087 and the maximum and minimum values were 9610 and 5954.Next, FIG. 19( ) shows a full-track profile measured when a headposition signal is varied and a reference profile. After 20 times ofmeasurement, the average of the RMS values was 20020 and the maximum andminimum values were 24155 and 16912. If the upper limit of the RMS valueis set to about 12000, it would be possible to detect a variation of thehead position signal surely. The RMS value described here is a unit usedinside computers and real values are not discussed.

Furthermore, a description will be made for a processing carried out ifthe magnetized state of the read-back element is disturbed, thereby theoutput of the position signal is judged to be varied. If the retry countexceeds a predetermined value in step 6, it is judged that the headposition signal is stabilized enough. Thus, a routine for regeneratingthe correction table of the position signal is called in step 7. Theprocess for creating the correction table of the position signal is thesame as that described in the embodiment 3.

If the retry count is judged to be within the predetermined value instep 6, control goes to the retry processing. In this retry processing,the head is instructed to seek a zone where no user data exists and awrite operation (dummy write operation) is carried out so as to apply anexternal magnetic field to the read-back element intentionally. Afterthe dummy write operation, the same processes in step 2 and after arerepeated. If the normal state is not restored after the dummy writeoperation, the sense current (Is) applied to the read-back element isincreased or decreased, thereby improving the effect of the dummy writeoperation. In stead of the dummy write operation employed for restoringthe read-back element to the normal state here, a more complicatedprocess may be employed so as to improve the effect of the retry.

Next, a description will be made for a method for detecting a propertyvariation of the read-back element of the head with use of a pattern fordetection micro-track profile with reference to FIG. 20.

In steps 1 to 3 shown in FIG. 20(A), the head is instructed to seek atrack width measuring zone and follow up the track, thereby amicro-track profile is detected from the pattern for detectionmicro-track profile. The processes are the same as those described inthe embodiment 2. In step 4, the RMS value is calculated from betweenthe detected micro-track profile and the reference profile. Thereference profile is a value measured for each head beforehand andwritten in the memory of the package board 17 or in part of themanagement area of the disk 12. In step 5, the RMS value is comparedwith the upper limit value. If the RMS value is within the upper limitvalue, the state is judged to be normal and the processing is finished.

FIG. 20B shows a micro-track profile measured at a normal time and thereference profile. After 20 times of measurement, the average of the RMSvalues was 1435. The maximum and minimum values were 1857 and 1040.Next, FIG. 20C shows a micro-track profile measured when a propertyvariation occurs in the read-back element and the reference profile.After 20 times of measurement, the average of the RMS values was 2821.The maximum and minimum values were 3598 and 2124. If the upper limit ofthe RMS value is set to about 2000, it would be possible to detect aproperty variation of the read-back element surely. The RMS valuedescribed here is a unit used inside computers and real values are notdiscussed.

Furthermore, a description will be made for a processing to be executedif the RMS value exceeds the upper limit value and the magnetized stateof the read-back element is disturbed, thereby a variation is detectedin the property. If the retry count exceeds a preset value in step 6,the read-back element head position signal is possibly stabilizedenough, so that a routine for learning the initial values of variousparameters for the signal processing is called in step 7.

If the retry count is still within the preset value in step 6, controlgoes to the retry processing. The retry processing is executed with useof a method that lets the head seek a zone where no user data exists,then execute a write operation (dummy write), thereby applying anexternal magnetic field to the read-back element intentionally. Afterthat dummy write operation, the processings in step 2 and after arerepeated. If the normal state is not restored with a dummy writeoperation, the sense current (Is) applied to the read-back element isincreased/decreased, thereby improving the effect of the dummy writeoperation. In stead of the dummy write operation process employed tonormalize the read-back element in this embodiment, a more complicatedprocess may also be employed to improve the effect of the retry more.

According to this embodiment, therefore, because it is possible todetect a phenomenon that the magnetized state of the read-back elementis disturbed, thereby the position signal output is varied, it ispossible to avoid such a fatal error as overwriting an adjacent datatrack as a result of write operation offset from the target data track.Thus, the reliability of the magnetic recording disk apparatus has cometo be improved significantly. In addition, even when the position signaloutput is varied, the position signal correction table is recreated,thereby the same head positioning accuracy as that before the variationoccurs can be kept as is. Consequently, the track density of themagnetic recording disk apparatus has been improved successfully. Inaddition, because a property variation of the read-back element can bedetected only by reading back a detection pattern, it is possible toreduce such a recovery processing time as dummy write operation, etc.,thereby enabling the access performance of the magnetic recording diskapparatus to be improved more.

Furthermore, because it is possible to reduce error occurrence bycorrecting the non-linearity of the head position signal caused by thedegradation of the sensitivity at the end part and disturbance of themagnetizing direction of the head read-back element, the headpositioning accuracy can be improved more. In addition, because it ispossible to detect a property variation of the read-back element relatedto a variation of the head position signal surely and correct thevariation level, the reliability of the head positioning can be improvedsignificantly.

The present invention, therefore, can provide a magnetic recording diskapparatus that has increased the data track density in the radialdirection, thereby having improved both of the storage capacity and thereliability successfully.

What is claimed is:
 1. A magnetic recording disk apparatus, comprising:a magnetic recording disk medium having a plurality of tracks formedthereon in a concentric circle pattern; a plurality of servo areas, ineach of which a servo pattern is recorded, formed in said tracks; a dataarea formed between the servo areas; a plurality of micro-servo areasdisposed in said data area, each of which divides said data area intoseveral different areas; and a plurality of patterns disposed betweeneach of said micro-servo areas; a magnetic head including a read elementand a write element; a servo decoder for generating a head positionsignal from said servo pattern; and means for correcting a deviation ofthe head position by detecting a signal from said plurality of patterns;wherein a length of each of said plurality of patterns in the tracklength direction is less than a length between said micro-servo areas, awidth of said plurality of patterns in the track width direction is lessthan a track width of said data area, and an area of each saidmicro-servo area is smaller than that of each said servo area.
 2. Amagnetic recording disk apparatus according to claim 1; wherein aplurality of said patterns are disposed on two or more tracks.
 3. Amagnetic recording disk apparatus, comprising: a magnetic recording diskmedium having a plurality of tracks formed thereon in a concentriccircle pattern; a plurality of servo areas, in each of which a servopattern is recorded, formed in said tracks; a data area formed betweenthe servo areas; a plurality of micro-servo areas disposed in said dataarea, each of which divides said data area into several different areas;and a plurality of patterns disposed between each of said micro-servoareas; a magnetic head including a read element and a write element; aservo decoder for generating a head position signal from said servopattern; and means for correcting a deviation of the head position bydetecting a signal from said plurality of patterns; wherein a length ofeach of said plurality of patterns in the track length direction is lessthan a length between said micro-servo areas, a width of said pluralityof patterns in the track width direction is equal to a track width ofsaid data area, and an area of each said micro-servo area is smallerthan that of each said servo area.
 4. A magnetic recording diskapparatus according to claim 3; wherein a plurality of said patterns aredisposed on two or more tracks.